I have recently had my motor rebuilt it is making a rattle sound from the top end like a detonation sound almost. The truck isn't throwing any codes. I have had it in the shop several times and it has been tore apart again with no signs of anything loose or damaged. I think I may have an issue with the air/fuel mix as the rattle seemed to get worse at higher elevations and on my return trip home as I came back to a lower elevation it seemed to quiet down. It only makes the noise part of the time and when you floor it it's all there no noises at all. Can anyone give me advice on what to look at? Sorry for not stating what it is....2012 f150 5.0..new everything on the rebuild except for cams and crank as they were in good shape. even with the higher octane fuel it is still producing the detonation sound just not as loud.

 

Perhaps you need to select a higher octane fuel.
.

 

.

If the higher octane doesn't work maybe....
Don't know this for a fact that your engine (which you don't describe or even the year) has one but if so could be a bad or disconnected knock sensor.

 

That's backwards. Less air at high altitude. Lower cylinder pressure. Less knocking.

If you hadn't said it was engine knock I would have suspected cam chain / tensioner issues assuming it's OHC (didn't see any info on truck or engine).

 

I edited the post. with the rebuild it got new chains and tensioners along with cam phasers only the cams and crank were reused new everything else internally.